The present invention relates to the general field of making gas turbine casings out of composite material, and more particularly of making fan retention casings for aeroengine gas turbines.
In a gas turbine aeroengine, a fan casing performs several functions: it defines the inlet passage for admitting air into the engine, it supports an abradable material in register with the tips of the fan blades, it optionally supports a structure for absorbing soundwaves in order to provide acoustic treatment at the inlet of the engine, and it incorporates or supports a retention shield. The shield constitutes a trap for retaining debris such as articles that have been ingested or fragments of damaged blades that are projected outwards by centrifuging, for the purpose of preventing them from passing through the casing and striking other portions of the aircraft.
It is common practice for a fan retention casing to be made of a relatively thin wall defining the air inlet passage and supporting an abradable material in register with the path followed by the tips of the fan blades, together with the acoustic treatment coating, if any, and by a shield structure that is fastened to this wall on its outside, in register with the fan.
Proposals have already been made to make a fan retention casing out of composite material. By way of example, reference may be made to document EP 1 961 923, which describes fabricating a casing of varying thickness out of composite material comprising forming fiber reinforcement in the form of superposed layers of a fiber texture and densification of the fiber reinforcement by means of a matrix. More precisely, that document provides for using a takeup mandrel for use in three-dimensionally weaving the fiber texture, with the texture then being wound as superposed layers onto an impregnation mandrel presenting both an outside surface of profile corresponding to the profile of the central portion of the casing that is to be fabricated, and also two side plates corresponding to the fastener flanges of the casing. The fiber preform as obtained in this way is held on the impregnation mandrel and it is impregnated with resin, which resin is then polymerized.
Practical performance of that method raises the problem of transferring the fiber texture from the takeup mandrel onto the impregnation mandrel. In order to solve that problem, the Applicant has made proposals in French patent application FR 11/53212 (not yet published) for a winding machine that makes it possible, while transferring the fiber texture from the takeup mandrel to the impregnation mandrel, simultaneously to position the fiber texture correctly on the impregnation mandrel and to apply an appropriate winding tension.
With such a machine, there is a problem of cutting the fiber texture at the end of winding. That operation requires a cutting tool to be positioned very accurately in order to avoid any inaccuracy in the cutting, which would have the consequence of creating a localized zone that is either too rich in fibers (cut too long), or else too rich in resin (cut too short).